1) Field of the Invention
The present invention relates to an electroconductive adhesive and an adhesive article using the same and in particular to an adhesive for labels stuck on integrated circuit chips or electronic parts.
2) Description of the Related Art
Generally, labels used for electronic circuit elements are provided with a printing surface on the front and an adhesive layer made of a pressure-sensitive adhesive on the back, and the labels are stuck on electronic circuit parts to display tracking information and identification information on the parts.
The material constituting these labels is originally electrically insulated or not electroconductive so that upon release of the labels from liners, static electricity is generated, and its electric charge can be accumulated and discharged to damage parts therearound.
Generation of static electricity is a serious problem that causes breakdowns and damages to electrical circuit elements. Static electricity is generated as a result of imbalance in electric charges between the surfaces of articles (particularly insulators) upon being rubbed against each other or upon being released. These electric charges are accumulated on the surface of insulators to appear as static voltage. When the static voltage is high, the static electric charge is discharged all at once to cause the breakdown of articles as well as the internal breakage of electronic parts, semiconductor wafers etc.
For preventing or reducing a risk for frictional electricity to be charged, the labels are composed preferably of an electroconductive material. If the adhesive used therein is electroconductive, electric charges can be dissipated without damage.
As the technique of endowing such an adhesive with electrical conductivity, a technique described in Japanese Patent Application Laid-open No. H8-253755 is known.
The technique described in Japanese Patent Application Laid-open No. H8-253755 is constituted such that an electroconductive polymeric compound is mixed with an adhesive to give electrical conductivity to the adhesive, but the technique described in this publication cannot achieve electrical conductivity unless the polymeric compound is added in a large amount. When the polymeric compound is added, there is also a problem that the original adhesiveness of the adhesive is reduced.
As will be described later, it cannot be recognized that addition of the electroconductive polymer (polyaniline) in a very small amount (0.1 wt %) makes little difference in the electrical conductivity of most of adhesives.
As another general method of endowing an adhesive with electrical conductivity, a method that involves dispersing an electroconductive material such as metallic powders or particles of copper, silver, nickel, aluminum or tin in an adhesive has been adopted.
In these methods, however, there is still a problem that sufficient electrical conductivity cannot be achieved when the content of the electroconductive material in the adhesive is low, and thus a large amount of the electroconductive material should be contained in the adhesive. Accordingly, there are problems such as a reduction in adhesiveness of the adhesive and difficult applicability to the electronic parts/IC manufacturing industry owing to a high content of metallic particles and powders. Because the adhesive is disposed together with paper, film etc., there is also a problem such that, when metallic powders and particles are contained therein, the burden is put on the environment.
The present invention has been achieved in order to solve the above problems, and an object of the invention is to provide an electroconductive adhesive having a heme protein mixed in a very small amount thereby exhibiting electrical conductivity without deteriorating adhesion, which is used on the surface of electronic parts or a label thereby preventing and eliminating static electricity and improving the efficiency of heat dissipation, as well as an adhesive article using the same.